All thhree Windows OS support Windows networking, which is simply NetBIOS
over TCP/IP.
I have a Windows 98 machine up and running on a network of Windows XP and
Vista.
I can see and access Windows 98 shares from Windows XP
I can see and access Windows 98 shares from Windows Vista.
I can see and connect to Windows XP (Home or Pro) machines and access shares
from Windows 98.
I can see, but NOT connect to Windows Vista from Windows 98.
I can only conclude that Microsoft simply put in code specifically to reject
connections from Windows 98 to Vista.
I agree that it looks that way. But I don't think that Vista looks at
connection requests, checks for Windows 98, and intentionally rejects
them.
Rightly or wrongly, Microsoft decided that networking compatibility
with Windows 95/98/Me wasn't required in Vista.
Those Windows versions don't have the necessary code to interface with
Vista's networking and security models. That code is in the versions
derived from Windows NT: Windows 2000, XP, Vista, and 7.
--
Best Wishes,
Steve Winograd, MS-MVP (Windows Desktop Experience)
Microsoft Most Valuable Professional Program
http://mvp.support.microsoft.com